Impaired glucose tolerance represents a category of results from glucose tolerance tests that is not completely normal nor meets criteria for NIDDM. About half of all subjects found to have IGT progress to NIDDM over time with a rate of about 5% per year. The purpose of this randomized, prospective multicenter clinical trial is to determine whether the progression from IGT to NIDDM in high risk populations can be prevented or delayed with specific interventions, including intensive lifestyle change and metformin.